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Biomedical subjects

N Doba

Publications and source records attributed to N Doba.

At least 73 records · Page 4Linked to original sources
PubMed1978

Regional distribution of blood flow during arterial hypertension produced by lesions of the nucleus tractus solitarii in rats.

Changes in the fractional distribution of cardiac output (FF), organ blood flow, and regional vascular resistance were measured by the isotope dilution technique of Sapirstein using 86Rb as indicator in unanesthetized rats during acute arterial hypertension produced by bilateral lesions of the nucleus tractus solitarii (NTS). After NTS lesions, the FF was significantly reduced in skin, muscle, and colon, increased in ventricular myocardium, spleen, and adrenal glands, and was unchanged elsewhere. Because of a marked reduction in cardiac output (CO) during hypertension, the absolute organ blood flow (FF X CO) was reduced in lesioned rats to 30-40% of control in skin, muscle, and colon and between 60% and 75% of control in most of the remainder of the gastrointestinal tract and renal cortex; it was unchanged in myocardium and endocrine glands. Resistance was substantially increased (4- to 6-fold) in skin, muscle and colon but was only moderately increased (1.5- to 2.5-fold) in the remaining organs. The results indicate that, while NTS lesions will increase resistance in most vascular beds, the response is unequally distributed, influencing skin, muscle, and colon disproportionately to other tissues. Because of an interaction between a reduction in CO and little autoregulation, blood flow is reduced primarily in skin, muscle, and colon. The pattern of redistribution of CO was consistent with the interpretation that NTS hypertension results from interrupting baroreceptor reflexes centrally. The pattern of redistribution of blood flow in rats with NTS lesions differs from that produced by deoxycorticosterone acetate-salt and renal ischemia.

Animals↗
PubMed1976

Catecholaminergic axo-axonic synapses in the nucleus of the tractus solitarius (pars commissuralis) of the cat: possible relation to presynaptic regulation of baroreceptor reflexes.

A study was performed on adult cats to investigate synaptic structures of nerve terminals in the commissural portion of the nucleus of the tractus solitarius (NTS); a site where the cardiovascular afferent fibers terminate and where a dense plexus of adrenergic element also resides. Synaptic contacts observed in the commissural portion were predominantly axo-dendritic but a smaller number of axo-somatic synapses were also recognized. A third type of junction, axo-axonic, appears to be unique to the commissural portion of the nucleus, since no axo-axonic contacts were encountered in the medial and ventrolateral portions of the NTS. By labeling with the 'false' neurotransmitter 5-hydroxydopamine (5-OHDA), three types of axo-axonic contacts with different presynaptic components could be identified; namely, axon varicosities with small clear spherical vesicles, axon varicosities containing flat synaptic vesicles and others with small cord vesicles labeled with 5-OHDA. Postsynaptic components were always axon varicosities with clear spherical vesicles. After surgical denervation of the IXth and Xth cranial nerves, no degenerated axon varicosities were observed in the presynaptic side in the axo-axonic contact. The present study clearly demonstrates that the commissural portion of the NTS contains axo-axonic synapses and some of the adrenergic axons in this area provide the presynaptic components for this type of synapse. Possible roles of adrenergic nerves to presynaptic regulation of baroreceptor reflexes are discussed.

Animals↗
PubMed1975

Changes in regional blood flow and cardiodynamics associated with electrically and chemically induced epilepsy in cat.

Changes in cardiodynamics and regional blood flow were examined in chronically prepared paralyzed cats during seizures induced electrically by transcerebral or direct cortical stimulation or by administration of flurothyl ether (Indoklon) or pentylenetetrazol (Metrazol). Transcerebral and chemical stimuli produced the greatest vascular responses. During seizures there was an abrupt elevation of arterial pressure unassociated with consistent changes in heart rate. Vascular resistance was increased in femoral, renal and mesenteric arteries with variable reductions in blood flow. Resistance was decreased and flow passively increased in the common carotid artery reflecting the loss of cerebral autoregulation. Cardiac output was unchanged. With seizures associated with large elevations of arterial pressure, the central venous and left ventricular end-diastolic pressures were markedly increased indicating incipient congestive failure. The pressor response was blocked by alpha-adrenergic blockade with phentolamine. Increased regional vascular resistance was abolished by regional sympathectomy. While either adrenalectomy or treatment with 6-hydroxydopamine alone failed to abolish the pressor response, combined, they did. Such treatment unmasked an atropine-sensitive bradycardia. The pressor response with seizures is a consequence of increased vascular resistance in viscera and muscles due to widespread activation of sympathetic neurons and release of adrenomedullary catecholamines. Co-activation of cardiovagal and cardiosympathetic neurons may underlie some associated arrhythmias. Cardiovascular events may severe, by redistribution of the cardiac output, to assure increased availability of oxygen and nutrients to brain to meet the metabolic demands of convulsions.

Adrenalectomy↗
PubMed1975

The synaptic structure of catecholaminergic axon varicosities in the dorso-medial portion of the nucleus tractus solitarius of the cat: possible roles in the regulation of cardiovascular reflexes.

The study was performed on adult mongrel cats to investigate synaptic structures of nerve terminals in the dorso-medial portion of the nucleus tractus solitarius (NTS), where majorities of the cardiovascular afferent fibers terminate and a dense plexus of the catecholaminergic nerves exists. In normal control groups, axo-dendritic and axo-somatic contacts were commonly observed but no axo-axonic contacts were seen. Synaptic vesicles were almost exclusively spherical (97%) and less frequently flat (3%). Small cored vesicles were not observed in animals with formalin-glutaraldehyde and osmium tetroxide fixation. Two or three days after denervation of IXth and Xth cranial nerves, degenerated axon varicosities occupied about 15-20% of total population. Quantitative analysis after intracisternal injection of 5-hydroxydopamine revealed 3 different types of the varicosity: varicosities with spherical clear vesicles (85%), flat clear vesicles (3%) and small cored vesicles (12%). Axon varicosities with small cored vesicles predominantly exhibited axo-dendritic synapses and occasionally showed the closed apposition with those containing spherical clear vesicles. 6-Hydroxydopamine produced a minimal degree of degenerative changes in some axon varicosities (less than 5%). Treatment with 5-hydroxydopamine after IXth and Xth cranial nerve section gave intact axon varicosities with small cored vesicles. In conclusion, there is a relatively dense innervation of catecholaminergic nerves in the dorso-medial portion of the NTS, which apparently does not stem from the IXth and Xth cranial nerves. Possible roles of catecholaminergic nerves are discussed.

Animals↗
PubMed1975

Changes in cyclic nucleotide metabolism in aorta and heart of neurogenically hypertensive rats: possible trigger mechanism of hypertension.

Changes in cyclic nucleotide metabolism similar to those characteristic of the chronic forms of hypertension were observed in an acute neurogenic form of hypertension in rats produced by electrolytic lesions of the nucleus tractus solitarii. These changes that were evident 2 hr after the lesions were made included decreased cyclic AMP levels in the heart, increased cGMP:cAMP ratio, cAMP phosphodiesterase (3':5'-cAMP 5'-nucleotidohydrolase, EC 3.1.4.17) and guanylyl cyclase (GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2) activities in the aorta and decreased snesitivity of adenylyl cyclase (ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1) in both the aorta and heart to stimulation by the beta-adrenergic stimulant isoproterenol. These changes appear to depend on catecholamine release and are not due to mechanical distortion secondary to the increased arterial pressure. These studies provide biochemical support to the concept that the sympathetic nervous system may play a critical role in the initiation of the hypertensive syndrome and that chronic hypertension could result from the fixation of the biochemical effects of increased sympathetic activity.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1973

Predatory attack, grooming, and consummatory behaviors evoked by electrical stimulation of cat cerebellar nuclei.

Electrical stimulation at single sites in the rostral fastigial nucleus elicits hypertension, grooming, feeding, and attack behaviors in the cat. The stimulus intensity and availability of suitable goal objects determines the behavior. Bilateral lesions of the area fail to produce motor deficits. The rostral fastigial nucleus may be a cerebellar area for behavioral and autonomic regulation.

Aggression↗